Environment Research Institute, Shandong University, Jinan 250100, PR China; State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Science, Beijing 100012, PR China.
Chemosphere. 2013 Nov;93(9):2004-10. doi: 10.1016/j.chemosphere.2013.07.021. Epub 2013 Aug 12.
Levoglucosan is a typical molecular tracer of biomass-burning aerosols in the atmosphere. The mechanism for OH-initiated reaction with levoglucosan is studied at the level of MPWB1K/6-311+G(3df,2p)//MPWB1K/6-31+G(d,p). The possible subsequent reactions in the presence of O2, NO and H2O are also taken into consideration. The study shows that the H atom abstraction from the C4-position by the OH radical is an energetically favorable pathway, and that the OH-initiated products contribute to the formation of SOA and atmospheric acidity. The kinetic calculation is performed and the rate constants are calculated over the temperature range of 200-1500 K, using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The rate constant of levoglucosan reacting with the OH radical at 298 K is 2.21×10(-13) cm(3) molecule(-1) s(-1) and the atmospheric lifetime is 26 days ([OH]=2.0×10(6) molecule cm(-3)). The equilibrium constants both in gas phase and aqueous are computed. The free energy ΔG indicates that, the subsequent reactions tend to take place more spontaneously once the reaction occurs. This work provides a comprehensive investigation about OH-initiated atmospheric reactions with levoglucosan, which is helpful for experiment and risk assessment.
左旋葡聚糖是大气中生物质燃烧气溶胶的典型分子示踪物。在 MPWB1K/6-311+G(3df,2p)//MPWB1K/6-31+G(d,p)水平上研究了 OH 引发与左旋葡聚糖反应的机制。还考虑了在存在 O2、NO 和 H2O 的情况下可能发生的后续反应。研究表明，OH 自由基从 C4 位置夺取 H 原子是一种能量有利的途径，并且 OH 引发的产物有助于 SOA 和大气酸度的形成。使用 Rice-Ramsperger-Kassel-Marcus（RRKM）理论在 200-1500 K 的温度范围内进行了动力学计算，并计算了速率常数。在 298 K 时，左旋葡聚糖与 OH 自由基的反应速率常数为 2.21×10(-13) cm(3) molecule(-1) s(-1)，大气寿命为 26 天([OH]=2.0×10(6) molecule cm(-3))。计算了气相和水相中的平衡常数。自由能ΔG 表明，一旦反应发生，后续反应更倾向于自发进行。这项工作对 OH 引发与左旋葡聚糖的大气反应进行了全面的研究，有助于实验和风险评估。
